Parasympathetic nervous system: nerve cells of the autonomic nervous system that return the body to normal resting levels after adjustments to stress

Parathyroid glands: four pea-sized glands in the thyroid gland that produces parathyroid hormone to regulate blood calcium and phosphate levels

Parathyroid hormone (PTH): hormone produced by the parathyroid glands, which will increase calcium levels in the blood and lower the levels of phosphate

Peripheral nervous system (PNS): all parts of the nervous system, excluding the brain and spinal cord, that relay information between the central nervous system and other parts of the body

Peritubular capillaries: network of small blood vessels that surround the nephron.

Pituitary gland: gland at the base of the brain that, together with the hypothalamus, functions as a control center, coordinating the endocrine and nervous system

Polarized membrane: membrane charged by unequal distribution of positively charged ions inside and outside the nerve cell

Pons: region of the brain that acts as a relay station by sending nerve messages between the cerebellum and the medulla

Positive feedback: process by which a small effect is amplified.

Postsynaptic neuron: neuron that carries impulses away from the synapse

Presynaptic neuron: neuron that carries impulses to the synapse

Progesterone: female sex hormone produced by the ovaries that maintain uterine lining during pregnancy

Prostaglandins: hormones that have a pronounced effect in a small localized area

Protein hormones: group of hormones composed of chains of amino acids, that include insulin and growth hormone

Proximal tubule: section of the nephron joining the Bowmans capsule with the loop of Henle.

Reabsorption: transfer of glomerular filtrate from the nephron back into the capillaries

Reflex arc: neural circuit through the spinal cord that provides a framework for a reflex action

Refractory period: recovery time required before a neuron can produce another action potential

Renal pelvis: area where the kidney joins the ureter.

Repolarization: process of restoring the original polarity of the nerve membrane

Resting potential: voltage difference across a nerve cell membrane during the resting stage (usually negative)